1. Field of the Invention
This invention relates to a process of repairing a refractory body which process involves the step of projecting combustible particles in an oxygen-rich carrier gas against such body to cause oxidation of combustible particles in a reaction zone adjacent such body and thereby the generation of heat required for dressing such body or forming a refractory weld mass thereon.
The invention also relates to apparatus for use in carrying out such a process.
2. Description of the Related Art
The process may be of the type known as ceramic welding, in which refractory material is applied to a refractory substrate to form a coating thereon or to fill holes or fissures in its structure, or ceramic dressing, in which blocks or other forms of ceramic are shaped or cleaned by a cutting action.
Ceramic welding is a particularly important category of process falling within the invention. It is widely employed for repairing furnace linings in situ and has the advantage that durable refractory deposits can be formed at high furnace lining temperatures. Consequently repairs can be effected either without interrupting the furnace operation or with relatively short term interruption of its operation, depending on the type of the furnace and the position in the furnace where the repair is required.
The art of refractory mass formation by ceramic welding has been the subject of a lot of research and development work over the last two decades with a view to the attainment of ever higher qualities and reliabilities of the formed refractory deposits and with a view to utilising the welding technique for welding many different types of refractory composition and making it compatible with an increasing variety of operating parameters.
A particularly significant discovery, which heralded the birth of ceramic welding as a viable industrial process, was the importance of using oxidisable particles of an extremely small average grain size. Processes based on this discovery are disclosed in GB Patent 1 330 894.
The research and development work referred to has in part been concerned with the maintenance of a continuous feed of welding powder into a gas stream. The attainment of a consistently reliable feed of particulate material at a required feed rate involves various problems. Various means for solving these problems have been proposed, see e.g. GB Patent 2 173 715 and 2 103 959.
The handling of very fine easily oxidisable particles, e.g. particles of silicon or aluminium which are most often used as solid fuel constituents of ceramic welding or dressing powder, is attended by certain hazards. For example premature ignition or explosions can occur as a result of localised heating or electrical discharges due to friction in a particle feed line.
In ceramic repair processes there is frequently a need for rapid operations. This requires a high particle feed rate and high concentration of oxygen at the reaction zone. With increasing particle feed rates and oxygen concentrations however the risk of such hazards tends to increase. Notably hazardous conditions can occur when attempting to achieve a high feed rate of easily oxidisable particles directly into an oxygen-rich gas stream. The risk of premature ignition at the region where the particles encounter the oxygen-rich gas stream may be contributed to by mechanical forces.
It is important for the particle feed system for a ceramic repair process to be designed to reduce the risk of such accidents occuring where the particles are transferred from the powder store into an entraining gas stream.
In order to reduce accident risks, it has been proposed to avoid the use of oxygen-rich gas for entraining oxidisable particles from a store to a welding lance and to supply oxygen to the welding lance via a separate feed line (cf GB 2 035 524 and GB 2 180 047). In these proposals air and/or inert gas is used for entraining the particles from the store. A disadvantage of these proposals is the fact that for a given particle feed rate the larger the volume flow rate of the gas used for entraining the particles from the store, the lower the oxygen concentration at the reaction zone. The adoption of such proposed feed systems is therefore not conducive to the attainment of high particle feed rates and volume rates of formation of the refractory deposit. In the market for furnace repair work there is an important demand for a reduction in the time required for completion of this work and this demand cannot be satisfied when using the said previously proposed feed systems.